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Measurement of the semileptonic $CP$ asymmetry in $B^0-\overline{B}{}^0$ mixing

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Abstract

The semileptonic $CP$ asymmetry in $B^0-\overline{B}{}^0$ mixing, $a_{\rm sl}^d$, is measured in proton-proton collision data, corresponding to an integrated luminosity of 3.0 fb$^{-1}$, recorded by the LHCb experiment. Semileptonic $B^0$ decays are reconstructed in the inclusive final states $D^-\mu^+$ and $D^{*-}\mu^+$, where the $D^-$ meson decays into the $K^+\pi^-\pi^-$ final state, and the $D^{*-}$ meson into the $\overline{D}{}^0(\rightarrow K^+\pi^-)\pi^-$ final state. The asymmetry between the numbers of $D^{(*)-}\mu^+$ and $D^{(*)+}\mu^-$ decays is measured as a function of the decay time of the $B^0$ mesons. The $CP$ asymmetry is measured to be $a_{\rm sl}^d = (-0.02 \pm 0.19 \pm 0.30)\%$, where the first uncertainty is statistical and the second systematic. This is the most precise measurement of $a_{\rm sl}^d$ to date and is consistent with the prediction from the Standard Model.

Figures and captions

Mass distributions after weighting of (top) $ D ^-$ candidates in the $ D ^-$ $\mu ^+$ sample and of (bottom) $ D ^{*-}$ candidates in the $ D ^{*-}$ $\mu ^+$ sample, with fit results overlaid.

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Decay rate and charge asymmetry after weighting versus decay time for (top) the $ D ^-$ $\mu ^+$ sample and (bottom) the $ D ^{*-}$ $\mu ^+$ sample. The data from the two run periods and magnet polarities are combined and the fit results are overlaid. The number of bins in the asymmetry plots is reduced for clarity. The visible asymmetry in these plots can be fully attributed to the non-zero detection and production asymmetries (not to $ a_{\rm sl}^{d}$ ), as explained in the text.

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Animated gif made out of all figures.

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Tables and captions

Systematic uncertainties (in %) on $ a_{\rm sl}^{d}$ and $ A_{\rm P}$ for 7 and 8 $\mathrm{ Te V}$ $pp$ centre-of-mass energies. Entries marked with -- are found to be negligible.

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tex code
Table_1.pdf

Supplementary Material [file]

Supplementary material full pdf

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supplementary.pdf

This ZIP file contains supplemetary material for the publication LHCb-PAPER-2014-053. The files are: Supplementary.pdf : An overview of the extra figures *.pdf, *.png, *.eps, *.C : The figures in variuous formats

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Created on 11 July 2020.